Im sorry to hear this, it must be driving you mad as i know you hate the rattles.
I would be extremely surprised if this unit had blown or is clipping, i simply cannot even begin to think you could drive it hard enough within a confined space such as an SLS, so close to your head to generate enough volume to damage the unit or clip it.
I love my audio stuff and have had all sorts of speakers being driven from a valve amp and i've never experienced a blown speaker on a matched system even with ludicrous ear bleeding volumes.
My current system drives so much bass that it makes the candles on top of the speakers rattle and the picture frames on the coffee table rattle to name some things.
I even have a pair of B&O speakers in another room and they can get light unhinged stuff moving at high volume with their integrated subs.
So what i'm saying is, i am more likely to believe the base from them is either causing them to rattle against their housing or the frequencies produced is more likely to make surrounding trim rattle. I guess you could eliminate the housing by removing the sub and holding it but it would be more difficult to isolate a piece of surrounding trim. Sounds like you have a new sub coming your way so that might help remove that from the equation. A simple test might be to press down bits of trim to stop the vibration. I'm completely unfamiliar with an SLS interior and dont even know where the subs are.
But i hope you get it sorted!